This invention relates to a borehole logging apparatus for deep well drillings, with a device for transmitting measured data obtained while drilling from a borehole through the drilling fluid to the earth""s surface, with an elongated housing adapted for insertion in a drill string, a hydro-mechanical signal transmitter arranged in the housing and comprising a stator which is fixed to the housing and has at least one passage through which drilling fluid is routed from a side located upstream from the stator to a side located downstream from the stator, and a rotor mounted adjacent to the stator inside the housing for rotation about its longitudinal axis, said rotor having at least one continuous opening corresponding with the passage in the stator and being constructed to rotate either into a passing position in which the drilling fluid is allowed to pass through the passage and the opening aligned with it or into a throttling position in which a closed portion of the rotor throttles at least part of the flow through the passage in the stator, and a motor adapted to move the rotor repeatedly, in controlled intervals in response to signals indicative of the measured data to be transmitted, from the passing position into the throttling position and back into the passing position in order to generate in the drilling fluid a coded series of positive pressure pulses corresponding to the signals.
Apparatus of the type referred to are employed in particular in directional drilling in order to transmit measured data determined by measuring devices in the drill string while drilling to the earth""s surface and, on the basis of these measured data, to permit the progress and direction of drilling to be influenced to the desired extent.
From DE 41 26 249 A1 there is known an apparatus of the type initially referred to in which the hydromechanical signal transmitter is arranged in the upper end of a cylindrical housing. On its outside the housing has radially outwardly extending guide ribs to center it in the drill string, passages being provided between the guide ribs to form a bypass around the signal transmitter. On both sides of a disk-shaped rotor inside the housing there are provided several cylindrical bores which extend parallel to the housing axis and form the passages for the drilling fluid which can be throttled by the rotor. Downstream from the rotor the bores lead into radially outwardly inclined outlet bores which emerge in the shell surface of the housing. The known apparatus has proven itself under practical conditions. Experience has shown, however, that the solid particles entrained in the drilling fluid lead to erosion in the bores on account of the flow velocity and the change of flow direction caused by the necessary inclination of the outlet bores, which limits the useful life of the stator. A further disadvantage of the known apparatus is to be seen in the fact that the cross section of the passages in the stator and the openings in the rotor needed to achieve a sufficient amplitude of the pressure pulses places a lower limit on the possible outer diameter of the housing and obstructs a desirable further reduction of the housing""s outer diameter.
From U.S. Pat. No. 3,309,656 there is known an apparatus for the logging of boreholes while drilling and for the transmission of measured data in which continuous, frequency-modulated sonic waves transmitted by the drilling fluid are generated. This known apparatus is fixedly installed in the drill string and has at its upper end a transducer generating the sonic waves and comprising a stator sleeve equipped with longitudinal slots and a rotor rotatably mounted in the stator sleeve, the rotor having in its shell surface longitudinal grooves which are open at the top and whose lower ends lie in a passing position opposite the longitudinal slots so that the drilling fluid entering the longitudinal grooves of the rotor from above can exit at the lower end of the longitudinal grooves through the longitudinal slots of the stator. As the rotor is rotating, the longitudinal grooves are periodically closed by the wall portions of the stator located between the longitudinal slots so that sonic waves of varying frequency are generated in response to the rotational velocity of the rotor. Also in this known transducer part of the drilling fluid current is routed past the transducer through a bypass formed by a spider.
In a further borehole logging apparatus known from DE 196 27 719 A1 the signal transmitter is arranged at the lower end of the housing. In this apparatus the stator and the rotor of the signal transmitter are comprised of coaxially nesting sleeves which are open at their lower ends and have opposing longitudinal slots for creating passages adapted for controlled intermittent movement into an open position and a closed position.
It is an object of the present invention to provide a borehole logging apparatus of the type initially referred to which is equally suitable for use in small and large drill string bores and can be adapted by simple means to the particular drill string bore and the prevailing drilling fluid conditions so that with minimal throttling of the drilling fluid current the signal transmitter generates sufficiently significant pressure pulses for the transmission of signals. Furthermore, it is desirable that the borehole logging apparatus be insensitive to interference, long-lasting and easy to service.
This object is accomplished according to the present invention in that the housing has at its influx end a central inlet channel with an inlet opening and is sealed relative to the drill string by a sealing ring downstream from the inlet opening, that a feed pipe open at both ends with an outer diameter smaller than the inner diameter of the inlet channel is arranged to extend inside the inlet channel in the longitudinal direction of the inlet channel so that the current passing through it reaches the signal transmitter, that a bypass ring limiting the free annular cross section between the wall of the inlet channel and the feed pipe is arranged inside the inlet channel, and that downstream from the bypass ring the inlet channel has radial outlet openings through which a bypass current circulating around the feed pipe is routed out of the inlet channel into the drill string.
With the arrangement of the present invention it is possible to keep the outer diameter of the borehole logging apparatus so small as to be able to use the borehole logging apparatus with all deep drilling standard bores of coupling size 2xe2x85x9exe2x80x3 and larger and to be able to withdraw the apparatus from the derrick. Furthermore, the borehole logging apparatus is suitable on account of its small outer diameter for drill string bend radii of 40 feet. By changing the bypass ring and, where applicable, employing a feed pipe of larger diameter for use in drill strings of larger bore it is easy to adapt the bypass current to the various cross sections and flow velocities so that a sufficiently significant pressure pulse for the transmission of signals is always achievable. Conversion of the borehole logging apparatus for adapting to the particular flow conditions and drill string bore can be performed by the operators on the derrick and is easy and quick to accomplish. According to the present invention, the housing of the borehole logging apparatus can be split for this purpose at the point where the bypass ring is mounted and at the point where the feed pipe is mounted by undoing a threaded joint. Provision can also be made for the signal transmitter to have a beaker-shaped rotor with a symmetrical arrangement of radial slots and a cylindrical shell surface as well as a correspondingly slotted stator sleeve surrounding the rotor, which are located directly adjacent to the exit opening of the feed pipe and can be withdrawn from the housing by splitting the housing at the point where the feed pipe is mounted. Hence it is also an easy matter to examine the rotor and the stator sleeve of the signal transmitter and, if worn, to replace them with new parts by splitting the housing. According to the invention, the rotor is connected by a plug-in coupling to the end of the drive shaft and in axial direction is mounted solely on the drive shaft. Rotor friction is thus kept small and with it the amount of energy required to generate signals.
According to a further proposal of the invention, the inlet opening of the inlet channel is formed by a filter pipe which has radial filter openings and carries a catch hook at its free, closed end. Coarse contaminants in the drilling fluid are held back by the filter pipe so that they are unable to obstruct the bypass and the signal transmitter.
As set forth in DE 41 26 249 A1, movement of the rotor can be effected by a direct-current motor with reversible direction of rotation, the rotor being rotated back and forth between the passing position limited by a first stop and the throttling position limited by a second stop. To be able to switch off the motor exactly upon reaching the respective stop position and so prevent energy losses which occur when the motor remains activated briefly upon reaching the stop, the present invention provides for an angle-of-rotation transducer causing the motor to reverse each time upon reaching or shortly before reaching the stop position. To ensure that the motor is still reversed upon reaching the stop position even if the angle-of-rotation transducer is defective, added provision can be made, in accordance with DE 41 26 249 A1, for sensing the rise in motor current upon reaching the stop position, using this data to reverse the motor. As a further safety measure provision can be made for a time control device which effects the reversal of the motor after a specified time window, opened at the beginning of a rotor movement, has elapsed.